Variable magnification image projector

Abstract

An image projector is adapted to change the magnification of a projected image by moving a zoom lens with its focal length being changed, wherein the zoom lens is moved to and then stopped at a goal position from the initial position in the first direction. When it is desired to move the zoom lens to another goal position in the second direction opposite to the first direction as viewed from the initial position, the zoom lens is once moved to its reversal position beyond the second goal position and thereafter moved from the reversal position to the second goal position.

What is claimed is: 
     
       1. A variable magnification image projecting apparatus for projecting the image of an original onto a photosensitive member with a selected magnification, said apparatus comprising: a zoom lens for forming an image of the original on the photosensitive member;   lens drive means for moving said zoom lens along a predetermined path;   focal-length changing means for changing the focal length of said zoom lens in association with the operation of said lens drive means; and   control means for controlling said lens drive means such that in response to a selected magnification, said zoom lens is shifted to a goal position spaced away from an initial position of said zoom lens by a distance D and such that the focal length of said zoom lens is changed to a value corresponding to the selected magnification,   said control means controlling said lens drive means such that said zoom lens is moved through the distance D in the first direction when said goal position corresponding to the selected magnification is far in a first direction as viewed from said initial position and such that when said goal position corresponding to the selected magnification is far in a second direction opposite to the first direction as viewed from said initial position, said zoom lens is moved to a reversal position spaced away from said initial position by a distance (D+ΔD) in the second direction and then moved back by a distance ΔD is the first direction.   
     
     
       2. A variable magnification image projecting apparatus as defined in claim 1, wherein said control means includes clock pulse generating means and is adapted to count clock pulses generated by said clock pulse generating means and to control the movement of said zoom lens in accordance with the counted number of clock pulses. 
     
     
       3. A variable magnification image projection apparatus as defined in claim 2, wherein said control means is adapted to once move said zoom lens to one reference position after a power switch has been closed and then move said zoom lens from said reference position to a position corresponding to a predetermined magnification. 
     
     
       4. A variable magnification image projection apparatus as defined in claim 3, wherein said control means includes lens position detecting means for detecting said zoom lens when it reaches said reference position. 
     
     
       5. A variable magnification image projecting apparatus as defined in claim 2, wherein said clock pulse generating means is adapted to generate clock pulses in association with the operation of said lens drive means. 
     
     
       6. A variable magnification image projecting apparatus as defined in any one of claims 1, 2 and 5, wherein said focal-length changing means includes a first stationary member and a second movable member adapted to move and rotate in association with the movement of said zoom lens to change the focal length of said zoom lens, said second member being connected mechanically with said first member such that said second member will be rotated under the reaction of said first member during the movement of said zoom lens. 
     
     
       7. A variable magnification image projecting apparatus as defined in claim 6, wherein said first member is in the form of a cam member and said second member is in the form of a zoom ring member and wherein said second member is mechanically connected with said first member through a driven member which slidably engages said cam member. 
     
     
       8. A variable magnification image projecting apparatus as defined in claim 6, wherein said first member is in the form of a rack member and wherein said second member is mechanically connected with said first member through a gearing mechanism which engages said rack member. 
     
     
       9. A variable magnification image projecting apparatus as defined in claim 8, wherein said rack member is in the form of a helical rack member and said second member is in the form of a zoom ring member which includes a helical gear section engaging said helical rack member. 
     
     
       10. A variable magnification image projecting apparatus as defined in any one of claims 1, 2 and 5, wherein said lens drive means is selectively operable at a higher or lower speed and wherein said control means is adapted to operate said lens drive means at the higher speed until said zoom lens reaches a speed changing position forwardly spaced away from said goal position by a second predetermined distance when said goal position is in the first direction as viewed from said initial position and if said distance D is larger than the first predetermined distance, to operate said lens drive means at the lower speed during the movement of said zoom lens between said speed changing position and said goal position and to operate said lens drive means at the lower speed during the movement of said zoom lens between said initial position and said goal position when said goal position is in the first direction as viewed from said initial position and if said distance D is smaller than said first predetermined distance. 
     
     
       11. A variable magnification image projecting apparatus as defined in claim 10, wherein said control means is adapted to operate said lens drive means at the lower speed during the movement of said zoom lens between said reversal position and said goal position in the first direction. 
     
     
       12. A variable magnification image projecting apparatus as defined in claim 11, wherein said control means is adapted to operate said lens drive means at the higher speed until said zoom lens reaches a second speed changing position forwardly spaced away from said reversal position by a fourth predetermined distance and to operate said lens drive means at the lower speed until said zoom lens moves from said second speed changing position to said reversal position when said goal position is in the second direction as viewed from said initial position and if said distance D is larger than a third predetermined distance; and said control means is adapted to operate said lens drive means at the lower speed until said zoom lens moves from said initial position to said reversal position when said goal position is in the second direction as viewed from said initial position and if said distance D is smaller than said third predetermined distance. 
     
     
       13. A variable magnification image projecting apparatus for projecting the image of an original onto a photosensitive member with a selected magnification, said apparatus comprising: a zoom lens for forming an image of the original on the photosensitive member;   lens drive means for moving said zoom lens along a predetermined path, said lens drive means including a drive and a mechanism for transmitting a driving force from said drive to said zoom lens;   focal-length changing means mechanically connected with said drive for changing the focal length of said zoom lens in association with the operation of said lens drive means;   pulse generating means mechanically connected with said drive for producing clock pulses in association with the operation of said lens drive means; and   control means for counting clock pulses generated by said pulse generating means and for controlling a shift and focal length of said zoom lens to match the selected magnification in accordance with the counted number of clock pulses,   said control means controlling said lens drive means such that said zoom lens is moved from an initial position thereof through a distance D in a first direction when a goal position corresponding to the selected magnification is far in the first direction as viewed from said initial position and such that when said goal position is far in the second direction opposite to said first direction as viewed from said initial position, said zoom lens will be moved from said initial position to a reversal position spaced away from said initial position by a distance (D+ΔD) in the second direction and then moved from said reversal position through a distance ΔD in the first direction and wherein said distance D is a distance between said initial position and said goal position and said distance ΔD is a fixed distance independently of the selected magnification.   
     
     
       14. A variable magnification image projecting apparatus as defined in claim 13, wherein said focal-length changing means includes a first stationary member and a second movable member moving and rotating in association with the operation of said lens drive means to change the focal length of said zoom lens, said second movable member being mechanically connected with said first stationary member rotate under the reaction of said first member during the movement of said zoom lens. 
     
     
       15. A variable magnification image projecting apparatus as defined in claim 14, wherein said first member is in the form of a cam member and said second member is in the form of a zoom ring member and wherein said second member is mechanically connected with said first member through a driven member which slidably engages said cam member. 
     
     
       16. A variable magnification image projecting apparatus as defined in claim 14, wherein said first member is in the form of a rack member and wherein said second member is mechanically connected with said first member through a gearing mechanism which engages said rack member. 
     
     
       17. A variable magnification image projecting apparatus as defined in claim 16, wherein said rack member is in the form of a helical gear rack member and said second member is in the form of a zoom ring member having a helical gear section which engages said helical gear rack member. 
     
     
       18. A variable magnification image projecting apparatus as defined in any one of claims 13 through 17, wherein said drive is in the form of a reversible motor and wherein said control means is adapted to control the rotational direction and amount of said reversible motor matching the selected magnification. 
     
     
       19. A variable magnification image projecting apparatus as defined in any one of claims 13 through 17, wherein said control means is adapted to once move said zoom lens to one reference position after a power switch has been closed and then move said zoom lens from said reference position to a position corresponding to a predetermined magnification. 
     
     
       20. A variable magnification image projecting apparatus as defined in claim 19, wherein said control means includes lens position detecting means for detecting said zoom lens when it reaches said reference position. 
     
     
       21. A variable magnification image projecting apparatus as defined in claim 20, wherein said predetermined magnification is one. 
     
     
       22. A variable magnification image projecting apparatus as defined in claim 21, wherein said drive is in the form of a reversible motor and wherein said control means is adapted to control the rotational direction and amount of said reversible motor matching a selected magnification. 
     
     
       23. A variable magnification image projecting apparatus as defined in any one of claims 13 through 17, wherein said drive is in the form of a reversible motor which is selectively operable at a higher or lower speed and wherein said control means is effective such that when said goal position is in the first direction as viewed from said initial position and if said distance D is larger than a first predetermined distance, said reversible motor will be operated at the higher speed in a first rotational direction until said zoom lens reaches a speed changing position forwardly spaced away from said goal position by a second predetermined distance and operated at the lower speed in the first rotational direction during the movement of said zoom lens from said speed changing position to said goal position and such that when said goal position is in the first direction as viewed from said initial position and if said distance D is smaller than said first predetermined distance, said reversible motor will be operated at the lower speed in the first rotational direction until said zoom lens moves from said initial position to said goal position. 
     
     
       24. A variable magnification image projecting apparatus as defined in claim 23, wherein said control means is adapted to operate said reversible motor at the lower speed in the first rotational direction during the movement of said zoom lens from said reversal position to said goal position in the first direction. 
     
     
       25. A variable magnification image projecting apparatus as defined in claim 24 wherein said control means is effective such that when said goal position is in the second direction as viewed from said initial position and if said distance D is larger than a third predetermined distance, said reversible motor will be operated at the higher speed in the second rotational direction opposite to said first rotational direction until said zoom lens reaches a second speed changing position forwardly spaced away from said reversal position by a fourth predetermined distance and operated at the lower speed in the second rotational direction during the movement of said zoom lens from said second speed changing position to said reversal position and such that when said goal position is in the second direction as viewed from said initial position and if said distance D is smaller than said third predetermined distance, said reversible motor will be operated at the lower speed in the second rotational direction during the movement of said zoom lens from said initial position to said reversal position. 
     
     
       26. A variable magnification image projecting apparatus for projecting the image of an original onto a photosensitive member with a selected magnification, said apparatus comprising: zoom lens for imaging the image of the original on the photosensitive member;   lens drive means including a motor selectively operable at a higher or lower speed and a mechanism for transmitting a driving force from said motor to said zoom lens and said drive means moving said zoom lens along a predetermined path, said lens drive means being selectively operable at a higher or lower speed;   focal-length changing means mechanically connected with said lens drive means for changing the focal length of said zoom lens in association with the operation of said lens drive means, said focal-length changing means including a first stationary member and a second movable member moving and rotating in association with the movement of said zoom lens to change the focal length of said zoom lens, said second member being mechanically connected with said first member such that said second member will be rotated by the reaction of said first member during the movement of said zoom lens;   pulse generating means for generating clock pulses; and   control means for counting clock pulses generated by said pulse generating means and for controlling the shift and focal length of said zoom lens to match the selected magnification in accordance with the counted number of clock pulses,   said control means being such that when a distance D from the initial position of said zoom lens and a goal position of the same corresponding to be selected magnification is larger than a first predetermined distance, said lens drive means will be operated at the higher speed until said zoom lens reaches a speed changing position forwardly spaced away from said goal position by a second predetermined distance and operated at the lower speed during the movement of said zoom lens from said speed changing position to said goal position and such that when said distance D is smaller than said first predetermined distance, said lens drive means will be operated at the lower speed during the movement of said zoom lens from said initial position to said goal position.   
     
     
       27. A variable magnification image projecting apparatus as defined in claim 26, wherein said first predetermined distance is larger than said second predetermined distance. 
     
     
       28. A variable magnification image projecting apparatus as defined in claim 26, wherein said first and second predetermined distances are equal to each other. 
     
     
       29. A variable magnification image projecting apparatus as defined in claim 26, wherein said pulse generating means is mechanically connected with said motor to generate clock pulses in association with the operation of said motor. 
     
     
       30. A variable magnification image projecting apparatus as defined in claim 26, wherein said first member is in the form of a cam member and said second member is in the form of a zoom ring member and wherein said second member is mechanically connected with said first member through a driven member which slidably engages said cam member. 
     
     
       31. A variable magnification image projecting apparatus as defined in claim 26, wherein said first member is in the form of a rack member and wherein said second member is mechanically connected with said first member through a gearing mechanism which engages said rack member. 
     
     
       32. A variable magnification image projecting apparatus as defined in claim 31, wherein said rack member is in the form of a helical gear rack member and wherein said second member is in the form of a zoom ring member having a helical gear section which engages said helical gear rack.